1. Technical Field
The present invention relates to an image display device.
2. Related Art
In projection type image display device in recent years, a discharge lamp (e.g., extra-high pressure mercury lamp) is generally used as a light source.
However, in such a discharge lamp, there is a problem in that the lifetime of the discharge lamp is comparatively short, in that quick illumination is difficult, the scope of color reproducibility is narrow, and UV-light radiated from the discharge lamp causes degradation of a liquid crystal light valve, or the like.
As disclosed by Japanese Unexamined Patent Application, First Publication No. 2000-131762, a projection type image display device that includes a laser light source emitting a monochromatic light, has been proposed instead of the discharge lamp.
In this projection type image display device disclosed by the patent document, laser lights emitted from the laser light source are converted into parallel light by a convex lens, and the intensity distribution of the parallel light is uniformed.
The uniformed laser lights are incident onto a liquid crystal light valve, the intensity of the laser lights are modulated by the liquid crystal light valve, and the laser lights are subsequently projected on a screen through a convex lens arranged at a posterior in the image display device.
In the case in which the output power of the laser light source is not sufficient, the number of the laser beams can be increased (multi-beams) in order to solve the problem.
In a structure in which the number of the laser beam increases, a plurality of normal single emitter type laser light sources arranged side by side is used, or an arrayed multi-emitter type laser light source is used.
However, in the projection type image display device disclosed in the above described patent document, when the light source that emits the laser lights is used, the laser lights emitted from the light source are incident into the liquid crystal light valve (light modulation device) at a great angle with respect to the surface of the liquid crystal light valve, depending on the arrangement of the laser light sources.
If the incidence angle becomes greater, decreasing the F-number of the projection lens arranged at the posterior in the image display device is necessary. In this case, the cost of the projection lens increases.
Furthermore, if the incidence angle at which the laser lights which are incident into the liquid crystal light valve becomes greater, there is a problem in that the contrast of the image displayed onto the screen decreases.
Furthermore, when the laser lights are condensed into the liquid crystal light valve using a hologram element, the efficiency of illumination decreases due to an increase in diffraction loss, if a diffraction angle increases in the hologram element.